Adaptive Radiation In Living Reptiles

Adaptive Radiation In REPTILES

Adaptive radiation: Is rapid evolutionaryradiation. It is an increase in the number and diversity ofspecies. It produces more new species and those species live in a wider range ofhabitats.

Adaptive radiation leads to the formation of different species from a common ancestor by adopting various modifications for adaptation to different environment.

Reptiles displayed an amazing pattern of adaptive radiation in Triassic period (250-200 million years ago) ,co-related with the new ecological niches due to climatic and geologic changes .. hot to cooler temperature mountain building ,terrain transformation and varying plant lifeReptiles have shown the greatest evolutionary diversity of all vertebrate groups.

The stem reptiles Cotylosauria underwent considerable radiation During the Mesozoic Era (252 to 66 million years ) life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts roamed the Earth , this age is also known as the age of reptiles or the age of dinosaurs.Outstanding among the ancient reptiles were the DinosaursThe first Dinosaurs were small , meat-eating animals which evolved into thousands of different speciesMany got adapted to life on land with two legged gait and huge size example : Tyrannosaurus (6 meters height)

Some Dinosaurs became herbivorous swamp dwellers and reverted to four legged gait. The buoyancy of water allowed them to grow to enormous size , example : Brontosaurus ( 25 meters length)

The smallest fully-grown fossil dinosaur is the little bird-hipped plant-eater example : Lesothosaurus Lesothosaurus was a small, lightly-built dinosaur. It was an herbivore (plant-eater) and a fast, agile runner. It was small and lizard-like, about 3 feet (1 m) long. It walked on two long legs,had short arms, a long pointed tail, a flexible neck, and a small head. Its head was short and flat with large eyes. It had sharp, pointed front teeth and arrow-like cheek teeth, its lower jaw ended in toothless bone.

Many Dinosaurs developed protective devices like bony plates on the body Ex : Stegosaurus (6 meters long) or horns on the head Ex: Triceratops(6 meters long)

Stegosaurus Triceratops

Some ancient reptiles like Pterosaurus got adapted for aerial life.

Their wings were made of membrane of skin called patagium supported by the fore limds and greatly elongated 4th digit .Their hind limbs were weak and not used for walking MODERN REPTILES

Arboreal Adaptation: Among living modern reptiles there are numerous arboreal (tree dwelling) forms like geckos, calotes and chameleon. Arboreal adaptations were development of adhesive pads for climbing ,digit modification ( syndactyly in chameleon )or prehensile limbs and tail for climbing and clinging to branches

Aerial adaptation : Ancient reptiles like Pterosaurus got adapted to aerial life.The wings of these forms consists of a membrane of skin called patagium supported by the fore limbs and greatly elongated fourth digit .Hind limbs were weak. They had attained very large size -wing-size of upto 6 meters The size of volant or flying reptiles ranged from size of a sparrow to largest flying forms, but there is no perfect fossil record of Triassic lifeDraco has lateral extension of skin ,the patagium which helps in passive flight

Aquatic Adaptations

Certain ancient reptiles returned to water. Marine forms became fully adapted to aquatic mode of life. Plesiosaurus developed turtle-like body with long neck, they propelled through water with long paddle-shaped limbs Ex: Elasmosaurus Ichthyosaurus acquired fish-like body, with fin-like limbs Ex: Opthalmosaurus (21meters) Plesiosaurus,Mesosaurus,Ichthyo-saurus (extinct forms) and turtles, tortoise, crocodiles etc (living forms) show aquatic adaptations by developing paddle-like limbs,laterally compressed tail,false palate etc Hydrophis or sea snake has valvular nostrils and laterally compressed tail to aid in swimmingFossorial Adaptations

In thereptiles, adaptations for burrowing have also evolved independently many times. Tuatara and someturtlesmake burrows for themselves, but worm-like burrowing is seen in a diversity of forms within the squamates, the group comprising lizards, snakes and 'worm lizards.

Notable among the burrowing lizards are thesand-dwellingforms that inhabit arid regions of Africa, America and Australia. Amazingly they include species from six independent groups:geckos, iguanids, skinks, agamids ('dragon lizards'), gerrhosaurids ('plated lizards') and lacertids ('true lizards'). These lizards are capable of 'sand-diving' and move efficiently through sandy substrate with the help of fringes or spines on their toes, a pointed or spade-like snout, a cylindrical body and adaptations for breathing when submerged.

Among the snakes,. the Southern African burrowing aspAtractaspis bibronii) have independently evolved adaptations for burrowing into sandy soils, including smooth scales andfangsthat swing sidewards to inject prey within their tunnels.Astonishingly annelid-like are the aptly named 'worm lizards' oramphisbaenians, a lineage distinct from true lizards or snakes in which limb loss and head and skeleton morphology suited for an underground existence seem to have evolved several times. Examples include the limbless shovel-headedRhineura floridana, the keel-headedAnops kingiiandBipes bioporus, which has tiny forelimbs. Added to what we know ofamphibians, thesereptilesmake the convergent evolution of worm-like body plans even more compelling.As a final note on convergent burrowing mechanisms, the way in which many animals burrow also follows a specified 'burrowing cycle', which despite widely divergent anatomies basically relies on the same set of movements.

CreditsWiki pediaGoogleMap of Life - "Burrowing: from worms to vertebrates"http://www.mapoflife.org/topics/topic_37_Burrowing-from-worms-to-vertebrates/July 17, 2015